1. Field of the Invention
The invention relates to a fuel pump that pressurizes fuel for an internal combustion engine to a high pressure and then discharges it. More particularly, the invention relates to a plunger pump in which a valve that controls the flow and pressure of fuel is provided near a fuel pressurizing chamber of the plunger pump.
2. Description of the Related Art
Recently, among internal combustion engine for vehicles, so-called direct-injection types that inject fuel directly into the cylinders, even with spark-ignition systems, have become popular. Of these, some attempt to increase output by increasing the intake air amount by cooling the intake air through the vaporization heat of fuel injected into the cylinders during the intake stroke, and improve combustion stability during startup with semi-stratified combustion achieved by injecting fuel into the cylinders during the compression stroke.
In these type of internal combustion engines, compared with when the fuel is injected into the intake port, the fuel must be pressurized to a high pressure and then delivered to a fuel injection valve (i.e., a fuel injector), so a plunger type high pressure fuel pump is often used as the fuel pump.
Japanese Patent Application Publication No. 11-132131 (JP-A-11-132131), for example, describes one such fuel pump according to related art. The fuel pump described is a plunger pump that has a check valve that opens when the pressure on the fuel pressurizing chamber side is low provided in an intake side fuel passage that draws fuel into a fuel pressurizing chamber of the plunger pump. This check valve serves to prevent pulsations in the pressure of the fuel that is pressurized in the fuel pressurizing chamber, and also prevent hydraulic hammer caused by those pulsations from reaching the low pressure side. It is also known that this check valve is not limited to being a ball valve with little fuel intake resistance; it may also be a reed valve that can easily be made small.
Moreover, a fuel pump is also known (see Japanese Patent Application Publication No. 2001-355542 (JP-A-2001-355542), for example) that attempts to reduce the size of intake side and discharge side reed valves by forming both an intake side reed valve body and an discharge side reed valve body in the same valve plate, and forming intake side and discharge side valve seat holes that are opened and closed by these reed valve bodies in seat plates located on opposite sides of the valve plate, and controls the discharge amount and discharge pressure of fuel with the required accuracy by opening and closing an annular through-hole formed through the center portions of the valve plate and the seat plates with an electromagnetic spill valve.
Meanwhile, in a diesel engine, fuel injection with better fuel atomization and great penetrating force (i.e., in which the fuel particles travel far) is required, so a plunger pump capable of producing higher pressure is used for the fuel pump. However, in this case as well, a fuel pump in which an electromagnetic spill valve is provided near the fuel pressurizing chamber to control the discharge amount and discharge pressure of fuel is often used (see Japanese Patent Application Publication No. 2002-61548 (JP-A-2002-61548), for example).
In the related fuel pumps such as those described above, a check valve or a valve with that function must be provided on both the intake side and the discharge side. In recent years, however, relief valves or the like that limit the discharge pressure to a set pressure have also started to be housed in fuel pumps, so there is a need to consolidate functions in the fuel line.
However, when a plurality of valves are housed in a fuel pump in this way, and each of these valves is formed with a valve body, a valve seat, a spring, a guide, and a stopper, and the like, as a poppet valve or the like is, the number of parts becomes even larger and complicated hole-drilling must be performed on the pump housing, which increases costs.
In contrast, as described in JP-A-2001-355542, the number of parts and the amount of work on the pump housing can be reduced if the check valves on the intake side and the discharge side are formed by reed valves.
However, even in this case, the annular through-hole in the valve plate and the seat plates acts as a spillway for controlling the discharge amount and discharge pressure of the fuel and is opened and closed by a poppet valve type electromagnetic spill valve, which results in an increase in the number of parts and requires high precision valve seat hole drilling just the same, so costs are unable to be sufficiently reduced. Documents GB-A-1 219 762, EP 0 894 972 A2, US 2007/178529 A1, U.S. Pat. No. 3,070,022 and US 2003/095881 A1 disclose a system according to the preamble of the present invention. FR-A-704 918 discloses a mechanically controlled cam system for reducing impact load and enhancing fatigue strength of fins. Further, EP 1 541 942 A2 provides an expansion-type cryogenic refrigerator with a high-performance compressor for very low temperatures.